1. Field of the Invention
The present invention relates to a method of fabricating an optoelectronic integrated circuit chip, and more particularly, to a method of fabricating an optoelectronic integrated circuit chip, in which an optical absorption layer of a wave-guide type optical detector is formed to be thicker than a collector layer of a hetero-junction bipolar transistor by using a selective area growth by MOCVD (Metal Organic Chemical Deposition), and the wave-guide type optical detector and the hetero-junction bipolar transistor are integrated as a single chip on a semi-insulated InP substrate, thereby readily realizing the wave-guide type optical detector with an improved external quantum efficiency and having the ultra-high speed characteristics.
2. Description of the Related Art
In a conventional optical receiver chip mainly used in an optical communication system, as shown in FIG. 1, a long wavelength optical detector A having a typical PiN structure of p+InGaAs/n−InGaAs/n+InGaAs, and a hetero-junction bipolar transistor B having a structure of n+InP/p+InGaAs/n−InGaAs/n+InGaAs which is as same as that of PiN in part are integrated as a single chip on a semi-insulated InP substrate 10.
That is, the long wavelength optical detector A includes an n+InGaAs layer 21a, an n−InGaAs optical absorption layer 22a, a p+InGaAs ohmic layer 23a, a p-electrode 29 formed on the p+InGaAs ohmic layer 23a, and an n-electrode 30 formed on a predetermined region of the n+InGaAs layer 21a, which are sequentially stacked on the semi-insulated InP substrate 10.
Further, the hetero junction bipolar transistor B includes an n+InGaAs sub-collector 21b, an n−InGaAs collector layer 22b, a p+InGaAs base 23b, an n+InP emitter 24, and an n+InGaAs ohmic layer 25, which are sequentially stacked. Here, the n−InGaAs collector layer 22b and the p+InGaAs base 23b are formed on a predetermined region of the n+InGaAs sub-collector 21b. Further, the n+InP emitter 24 and the n+InGaAs ohmic layer 25 are formed on a predetermined region of the p+InGaAs base 23b. Also, an emitter electrode 26 is formed on the n+InGaAs ohmic layer 25, a base electrode 27 is formed on a predetermined region of the p+InGaAs base 23b, and a collector electrode 28 is formed on a predetermined region of the n+InGaAs sub-collector 21b. 
Meanwhile, a polymer layer 40 for protection and electrical insulation is formed on surfaces of the long wavelength optical detector A and the hetero-junction bipolar transistor B as described above. The polymer layer 40 is formed with a via hole to expose each electrode therethrough, so that the p-electrode 29 of the optical detector A and the base electrode 27 of the hetero-junction bipolar transistor B are connected to each other through an air bridge metal line.
As described above, the long wavelength optical detector having the foregoing simple PiN structure of p+InGaAs/n−InGaAs/n+InGaAs is not in need of an additional separate crystal growth process because crystal layers of the base, collector and the sub-collector of the hetero-junction bipolar transistor are formed as the same layer structure as PIN photodiode, so that this structure has been widely used.
In a current high-capacity ultra-high speed optical communication system, the optical detector is used to convert a ultra short optical signal pulse into an electrical signal, and then to amplify the converted electronic signal. Thus, the optical communication system should include a front end receiver having a complicated optoelectronic circuit for detecting and amplifying the ultra high speed optical signal, so that the manufacturing cost is increased. Consequently, it is difficult to economically fabricate an optical receiver with an excellent sensitivity.
In order to develop an economical ultra-high speed and long-distance high-capacity optical communication system, the optical receiver should be economically fabricated by a simple fabrication process. Further, in order to simplify the fabrication process of the optical receiver, it is preferable that a wave-guide type optical detector having both high quantum efficiency and ultra-high speed characteristics due to a thick optical absorption layer of waveguide structure formed by using a selective area growth by MOCVD, and a hetero-junction bipolar transistor capable of applying high gain characteristics to the converted electrical signal are integrated as a single chip on a semi-insulated InP substrate.
In addition, in the conventional structure, the optical absorption layer is configured to absorb surface incident light.